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Abstract:

The present invention relates to a hot-melt adhesive that comprises a
block copolymer having associative groups containing a nitrogen
heterocyclic compound. The invention also relates to block copolymers
having associative groups specifically adapted for implementation in a
hot-melt adhesive

Claims:

2. The adhesive as claimed in claim 1, wherein said copolymer comprises:
from 1 to 99% of at least one flexible block, and from 1 to 99% of at
least one rigid block.

3. The adhesive as claimed in claim 1, wherein the associative group is
chosen from an imidazolidonyl, triazolyl, triazinyl, bis-ureyl or
ureido-pyrimidyl group, preferably an imidazolidinyl group.

4. The adhesive as claimed in claim 1, further comprising at least one
tackifying resin.

5. The adhesive as claimed in claim 1, further comprising an additive
chosen from a plasticizer, a filler, a stabilizer and their mixtures.

6. A block copolymer, comprising: at least one block A composed of
monomers including: (i) at least one methacrylate of formula
CH2--C(CH3)--COOR1, where R1 is a linear or branched
C1-C3 alkyl group, a branched C4 group, a C3-C8
cycloalkyl group, a C6-C20 aryl group, a C7-C30
arylalkyl group including a C1-C4 alkyl group, a heterocyclic
group or a heterocyclylalkyl group including a C1-C4 alkyl
group, these groups optionally being substituted by one or more identical
or different groups chosen from hydroxyl and halogen groups, and/or (ii)
at least one styrene monomer, such as styrene, which is optionally
hydrogenated, and at least one block B including: (i) at least one alkyl
acrylate of formula CH2--CH--COOR2, where R2 is a linear
or branched C1-C12 alkyl group optionally substituted by one or
more identical or different groups chosen from hydroxyl and halogen
groups, and/or (ii) at least one methacrylate of formula
CH2--C(CH3)--COOR3 where R3 is a linear
C4-C12 alkyl group or a branched C5-C12 alkyl group,
and/or (iii) a diene monomer, such as butadiene or isoprene; said block
copolymer carrying an associative group based on nitrogenous heterocycle.

7. The copolymer as claimed in claim 6, wherein the block A comprises
methyl methacrylate monomers.

12. The copolymer as claimed in claim 6, wherein the copolymer is a
styrene/butyl acrylate/styrene block copolymer.

13. The copolymer as claimed in claim 6, wherein the mean number of
associative groups per copolymer chain is between 1 and 200 and
preferably between 1 and 30.

14. An adhesive comprising the copolymer as claimed in claim 6.

15. A method for improving the melt behavior of a hot-melt adhesive
and/or its adhesion to supports, comprising introducing therein a block
copolymer as defined in claim 6.

Description:

[0001] The present invention relates to block copolymers carrying
associative groups based on nitrogenous heterocycles and to hot-melt
adhesives comprising such a copolymer.

[0002] Hot-melt adhesives are thermoplastic materials which are solid at
ambient temperature and which become viscous liquids when heated. These
viscous liquids are applied to a first substrate and then it is covered
with a second surface. On cooling, adhesion between the substrate and the
second surface is obtained. The open assembly time is the period during
which the adhesive which has been applied to a substrate, which is
generally at ambient temperature, remains tacky, that is to say the
interval of time during which it is possible to apply the second surface
and, on cooling, to obtain adhesion between the substrate and the second
surface. Once this time limit for the open assembly time has been
exceeded, it is no longer possible to obtain sufficient adhesion between
the substrate and the second surface. These adhesives are denoted by the
abbreviation HMA (hot-melt adhesives). The present invention relates to
adhesives of this type.

[0003] Adhesives having an infinite open assembly time are of use for
self-adhesive labels or adhesive tape which are used at ambient
temperature. Depending on the nature of the adhesive, it is possible to
obtain more or less strong adhesions and, for example, to detach and
reattach the label. Bonding is achieved by pressure, often at ambient
temperature, hence the name for this category of adhesives, which are
referred to as "pressure-sensitive" or PSA (pressure-sensitive
adhesives). The adhesive is deposited on the substrate (for example label
or tape), either while hot, in the absence of any solvent, or while cold,
in the presence of a liquid vehicle which can be a solvent (solvent-based
adhesives) or water (water-based adhesives). When pressure-sensitive
adhesives are applied without a liquid vehicle, while hot, that is to say
at a temperature such that the adhesive flows, these adhesives are
denoted by the term HMPSA (hot-melt pressure-sensitive adhesives). They
are also sometimes denoted as self-adhesive hot-melt compositions. The
present invention also relates to adhesives of this type.

[0004] These hot-melt adhesive compositions generally comprise two main
constituents: a thermoplastic polymer (responsible for the good
mechanical and thermal properties and for at least a portion of the
adhesive properties) and a tackifying resin which plays a part in
improving the hot tack, the flowability or the wettability. Generally, a
number of additives are added thereto, such as plasticizers, including
oils, or waxes, stabilizers or fillers. Waxes (for example paraffin
waxes) make it possible to adjust the flowability, the open assembly time
and the setting time. Mention may be made, among the most widely used
thermoplastic polymers, of ethylene/vinyl acetate, ethylene/alkyl
(meth)acrylate or styrene/butadiene/styrene copolymers, atactic
poly-α-olefin (APAO), thermoplastic rubber, polyamide and others.
Tackifying resins belong chiefly to three main families: rosins (and
their derivatives), terpene resins and petroleum-derived resins
(aliphatic resins, aromatic resins and the like).

[0005] The inventors have shown that the use of a block copolymer carrying
associative groups based on nitrogenous heterocycle makes it possible to
improve the hot adhesion between two supports.

[0006] In particular, the inventors have shown that a specific copolymer
carrying associative groups based on nitrogenous heterocycle exhibits an
improved resistance to shearing as a function of the temperature in
comparison with the same copolymers not carrying associative groups.

[0007] Thus, such a copolymer provides the hot-melt adhesive comprising it
with an improved adhesion or even an adhesion similar to that of the
adhesives of the prior art on applying the adhesive according to the
invention at a lower temperature. This copolymer can also make it
possible to reduce the amount of tackifying resin to be added in order to
obtain an equivalent level of adhesion. These associative groups can also
confer a better mechanical strength and chemical resistance on the
adhesive.

[0008] A subject matter of the invention is thus a hot-melt adhesive,
comprising a block copolymer carrying associative groups based on
nitrogenous heterocycle.

[0009] Preferably, said copolymer comprises: [0010] from 1 to 99% of at
least one flexible block, and [0011] from 1 to 99% of at least one rigid
block.

[0012] Flexible block is understood to mean, within the meaning of the
present invention, a block for which the Tg is lower than ambient
temperature by at least 10° C.

[0013] The term "carrying" means, within the meaning of the present
invention, that the block copolymer and the associative groups are bonded
via one or more covalent bonds.

[0014] Rigid block is understood to mean, within the meaning of the
present invention, a block for which the Tg is greater than ambient
temperature by at least 20° C. Tg denotes the measured glass
transition temperature of a polymer, which can, for example, be measured
by DSC according to the standard ASTM E1356. By misuse of language, it is
also possible to speak of the Tg of a monomer in order to denote the Tg
of the homopolymer having a number-average molecular weight Mn of at
least 10 000 g/mol obtained by polymerization of said monomer. Thus,
sentences can be found where it is said that ethyl acrylate has a Tg of
-24° C. because homopoly(ethyl acrylate) has a Tg of -24°
C. All the percentages are given by weight, unless otherwise mentioned.

[0015] Preferably, the block copolymer is composed of a central block B
with a Tg<0° C. and of at least two rigid side blocks A and A'
with a Tg>40° C. In accordance with the definition given in
1996 by the IUPAC in its recommendations on the nomenclature of polymers,
block copolymer denotes a copolymer composed of adjacent blocks which are
constitutionally different, that is to say of blocks comprising units
derived from different monomers or from the same monomers but according
to a different composition or a different sequential distribution or a
different spatial configuration of the units. A block copolymer can, for
example, be a diblock copolymer, a triblock copolymer or a star
copolymer.

[0016] The block copolymer is, for example, a triblock copolymer A-B-A'
comprising a flexible central block B connected via covalent bonds to two
rigid side blocks A and A' (that is to say, positioned on each side of
the central block B), it being possible for A and A' to be identical or
different (this type of copolymer is also sometimes denoted A-b-B-b-A').

[0017] Preferably, the block copolymer is such that the rigid side
block(s) and the block B are incompatible, that is to say that they
exhibit a Flory-Huggins interaction parameter χAB>0 at
ambient temperature. This results in phase microseparation with formation
of a two-phase structure at the microscopic scale. The block copolymer is
then nanostructured, that is to say that domains are formed having a size
of less than 100 nm, preferably of between 10 and 50 nm. The
nanostructuring exhibits the advantage of resulting in a highly
transparent material, whatever the temperature.

[0018] The block copolymer can be obtained using polymerization techniques
known to a person skilled in the art. One of these polymerization
techniques can be anionic polymerization, such as is, for example, taught
in the following documents FR 2 762 604, FR 2 761 997 and FR 2 761 995.
It is also possible for the controlled radical polymerization technique
to be involved, which technique comprises several alternative forms
depending on the nature of the control agent which is used. Mention may
be made of SFRP (stable free radical polymerization), which uses
nitroxides as control agents and can be initiated by alkoxyamines, ATRP
(atom transfer radical polymerization), which uses metal complexes as
control agent and is initiated by halogenated agents, or RAFT (reversible
addition-fragmentation transfer), which for its part involves
sulfur-comprising products, such as dithioesters, trithiocarbonates,
xanthates or dithiocarbamates. Reference may be made to the general
review Matyjaszewski, K. (Ed.), ACS Symposium Series (2003), 854
(Advances in Controlled/Living Radical Polymerization), and to the
following documents for further details with regard to the controlled
radical polymerization techniques which can be used: FR 2 825 365, FR 2
863 618, FR 2 802 208, FR 2 812 293, FR 2 752 238, FR 2 752 845, U.S.
Pat. No. 5,763,548 and U.S. Pat. No. 5,789,487.

[0019] In order to obtain a triblock copolymer ABA' using the controlled
radical polymerization technique, use may advantageously be made of a
difunctional alkoxyamine of formula T-Z-T where the T groups are
nitroxides and the z group is a difunctional initiating group capable of
generating two initiating radicals. The starting action is a preparation
of the central block B by polymerizing, using the alkoxyamine, the
mixture of monomers resulting in the central block, which can be
described according to the notation employed above as T-B-Z-B-T. The
polymerization takes place with or without solvent, or else in dispersed
medium. The mixture is heated to a temperature greater than the
activation temperature of the alkoxyamine. When the central block B is
obtained, the monomer(s) resulting in the side blocks is (are) added. It
may be that, on conclusion of the preparation of the central block, there
remain monomers which have not been entirely consumed, which it may or
may not be chosen to remove before the preparation of the side blocks.
The removal can consist, for example, in precipitating from a nonsolvent,
recovering and drying the central block. If the choice is made not to
remove the monomers which have not been entirely consumed, the latter may
polymerize with the monomers introduced in order to prepare the side
blocks. Examples of the preparation of block copolymers by controlled
radical polymerization will be found in the following documents WO
2006/053984 or WO 03/062293. When the polymerization begins with the
formation of the block B, the two side blocks A and A' are identical in
terms of composition and of average molecular weight (the block copolymer
thus has the formula ABA).

[0020] As regards the central block B, the latter exhibits a
Tg<0° C. The number-average molecular weight Mn is between 10
000 and 1 000 000 g/mol, preferably between 10 000 and 50 000 g/mol (with
respect to a PMMA standard). The proportion by weight of the central
block B in the block copolymer is between 5 and 90%.

[0021] As regards the side blocks A and A', these exhibit a
Tg>40° C.

[0022] The copolymer of the invention can be functionalized with monomers
carrying associative groups introduced during the copolymerization; it
can also be grafted with associative groups after the polymerization
stage. The copolymer of the invention confers, on the adhesive
compositions of which it forms part, a very good cohesive and adhesive
behavior as a function of the temperature.

[0023] Preferably, the adhesive according to the invention additionally
comprises at least one tackifying resin.

[0024] This adhesive is generally deposited while hot over a substrate.

[0026] Other examples of rosin derivatives are described in Ullmann's,
Vol. A 23, pp. 79-86.

[0027] Mention may be made, as rosin derivatives, of those obtained by
hydrogenation, dehydrogenation, polymerization or esterification. These
derivatives can be used as is or in the form of polyol esters, such as
pentaerythritol, polyethylene glycol and glycerol esters.

[0028] Mention may also be made, as tackifying resin, of
dicyclopentadienes.

[0029] The presence of a copolymer carrying associative groups in the
adhesive which is a subject matter of the invention makes it possible to
improve the adhesion and the shaping of the adhesive. It is therefore
possible to obtain a bonding at a lower temperature for the same
effectiveness, in comparison with an adhesive not comprising such a
copolymer. This makes it possible to reduce the amount of tackifying
resin to be used in order to have the desired properties.

[0030] Thus, in a preferred embodiment of the invention, the adhesive
comprises from 1 to 70 parts of resin per 100 parts of the mixture of
copolymer and resin and preferably from 20 to 50 parts of resin per 100
parts of the mixture of copolymer and resin.

[0031] The adhesives which are subject matters of the invention can
additionally comprise one or more plasticizers as additive.

[0032] The plasticizers which can be used in the adhesives of the
invention are, for example, paraffinic, aromatic or naphthenic mineral
oils. They are used essentially to lower the viscosity and to contribute
tack. The amount of plasticizer can be between 10 and 30 parts per 100
parts of the mixture of adhesive.

[0033] Mention may also be made, as plasticizer, of phthalates, azelates,
adipates, tricresyl phosphate and polyesters.

[0034] The adhesives of the invention can also comprise fillers and
stabilizers as additives.

[0035] Mention may be made, as example of fillers, of silica, alumina,
glass, glass beads, calcium carbonates, fibers and metal hydroxides.
These fillers must not be so much as to reduce the tack or the mechanical
or adhesive properties of the adhesive after the application thereof. The
amount of fillers can represent up to 100 parts per 100 parts of
adhesive.

[0036] It is recommended to add stabilizers, such as antioxidants. Use may
be made of the normal antioxidants for thermoplastics.

[0037] The hot-melt adhesives of the invention are prepared by melt
blending at temperatures of between 130° C. and 200° C.
until a homogeneous mixture is obtained. The mixing time can be of the
order of from 30 minutes to 3 hours. Use may be made of the normal
devices for processing of thermoplastics, such as internal mixers,
extruders or rolls.

[0038] Another subject matter of the present invention is a block
copolymer, comprising: [0039] at least one block A composed of monomers
including: [0040] (i) at least one methacrylate of formula
CH2--C(CH3)--COOR1, where R1 is a linear or branched
C1-C3 alkyl group, a branched C4 group, a C3-C8
cycloalkyl group, a C6-C20 aryl group, a C7-C30
arylalkyl group including a C1-C4 alkyl group, a heterocyclic
group or a heterocyclylalkyl group including a C1-C4 alkyl
group, these groups optionally being substituted by one or more identical
or different groups chosen from hydroxyl and halogen groups, and/or
[0041] (ii) at least one styrene monomer, such as styrene, which is
optionally hydrogenated, and [0042] at least one block B including:
[0043] (i) at least one alkyl acrylate of formula
CH2--CH--COOR2, where R2 is a linear or branched
C1-C12 alkyl group optionally substituted by one or more
identical or different groups chosen from hydroxyl and halogen groups,
and/or [0044] (ii) at least one methacrylate of formula
CH2--C(CH3)--COOR3 where R3 is a linear
C4-C12 alkyl group or a branched C5-C12 alkyl group,
and/or [0045] (iii) a diene monomer, such as butadiene or isoprene; this
monomer may optionally have been hydrogenated after the polymerization;
said block copolymer carrying an associative group based on nitrogenous
heterocycle.

[0046] "Block copolymer" is understood to mean, according to the
invention, a linear or star block copolymer or, by extension, a gradient
copolymer. This copolymer is considered as a separate entity, in the
self-supported form, and not as a structure grafted to another
(co)polymer, such as the shell of a core-shell system conventionally used
as impact modifier.

[0047] Preferably, the copolymer according to the invention has an overall
polydispersity index PI=Mw/Mn (where Mw is its weight-average molecular
weight and Mn is its number-average molecular weight) ranging from 1 to
10 and preferably from 1.05 to 2.5.

[0048] The block A of the block copolymer according to the invention
preferably has a glass transition temperature of greater than 40°
C. It can, for example, comprise at least one monomer chosen from:
styrene and α-methyl-styrene, which are optionally hydrogenated,
methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl
methacrylate, isobutyl methacrylate, tert-butyl methacrylate or their
mixtures.

[0049] According to a preferred embodiment of the invention, the block A
comprises, indeed is even predominantly composed of, styrene monomer
units.

[0050] According to a preferred embodiment of the invention, the block A
comprises, indeed is even predominantly composed of, methyl methacrylate
monomer units.

[0051] In addition, it is possible for the block A to comprise, in
addition to the methacrylate or styrene, at least one dialkylacrylamide
monomer, the linear or branched alkyl groups of which independently
include from 1 to 10 carbon atoms, such as N,N-dimethyl-acrylamide.

[0052] As far as the block B is concerned, it preferably has a glass
transition temperature of less than 0° C. and more preferably of
at most -10° C.

[0054] According to a preferred embodiment of the invention, the block B
comprises, indeed is even predominantly composed of, n-butyl acrylate
and/or 2-ethylhexyl acrylate monomers and optionally, less preferably,
hydroxyethyl acrylate, 2-ethylhexyl methacrylate, n-octyl acrylate or
their mixtures.

[0055] According to a preferred embodiment of the invention, the block B
comprises, indeed is even predominantly composed of, diene monomers, such
as butadiene and/or isoprene. These monomers can be hydrogenated after
the polymerization.

[0056] A particularly preferred example of a block copolymer according to
the invention is a copolymer based on methyl methacrylate/n-butyl
acrylate/methyl methacrylate blocks. Another particularly preferred
example of a block copolymer according to the invention is a copolymer
based on styrene/n-butyl acrylate/styrene blocks. Another particularly
preferred example of a block copolymer according to the invention is a
copolymer based on styrene/butadiene/styrene blocks.

Associative Groups

[0057] "Associative groups" is understood to mean groups capable of
associating with one another via hydrogen, ionic and/or hydrophobic
bonds. According to a preferred form of the invention, the groups are
ones capable of associating via hydrogen bonds, comprising a nitrogenous
heterocycle, preferably a dinitrogenous heterocycle, generally comprising
5 or 6 atoms. Examples of associative groups which can be used according
to this preferred form of the invention are imidazolidonyl, triazolyl,
triazinyl, bis-ureyl or ureido-pyrimidyl groups. The imidazolidinyl group
is preferred.

Functionalization or Grafting of the Copolymer

[0058] According to one embodiment of the invention, the associative
groups can be introduced during the formation of the copolymer. This
embodiment is not limiting, it also being possible for a reactive
extrusion of a mixture of associative groups with the preformed block
copolymer to be envisaged.

Introduction During the Polymerization

[0059] The copolymers which are the subject matters of the invention carry
associative groups based on nitrogenous heterocycle. These associative
groups can be present both on the blocks A and on the blocks B or solely
on just one type of block A or B.

[0060] One way of modifying the base copolymers, so that they carry
associative groups based on nitrogenous heterocycle, is the
functionalization of the polymer during the polymerization thereof using
functional monomers capable of copolymerizing and therefore of being thus
inserted into the actual backbone of the polymer chains while carrying
said associative groups based on nitrogenous heterocycle. When this
method of functionalization by copolymerization is chosen in order to
obtain the block copolymer carrying associative groups according to the
invention, the functional monomers carrying the associative groups are
introduced, during the polymerization, as a mixture with the monomers
used to construct the block copolymer. Thus, for example, in the case of
a block copolymer according to the invention of ABA type, the functional
monomers carrying the associative groups can be introduced as a mixture
with the monomer or monomers constituting the blocks A and/or as a
mixture with the monomer or monomers constituting the block B.

[0061] Mention may be made, as examples of monomers which make possible
the introduction of imidazolidonyl groups into the polymer, of
ethylimidazolidone methacrylate and ethylimidazolidonemethacrylamide.

[0062] The copolymer which is the subject matter of the invention can thus
be obtained by controlled radical polymerization in the presence of a
nitroxide, as described in the application WO 03/062293.

[0063] Such a process can comprise the successive stages of:

1--preparing a monoalkoxyamine starting from a nitroxide, as described in
particular in the application WO 2004/014926, 2--preparing a
polyalkoxyamine, in particular a dialkoxyamine, starting from the
monoalkoxyamine obtained in stage 1, for example by reaction with an
α,ω-diol comprising ends esterified by a carboxyvinyl
compound, such as (meth)acrylic acid, 3--preparing the block B by
polymerization of the corresponding monomers in the presence of the
polyalkoxyamine obtained in stage 2, up to a degree of conversion
preferably of less than 90; optionally removing the residual monomers or
polymerizing the latter by conventional radical polymerization
techniques, 4--mixing the block B thus obtained with the monomers
intended to form the block A, 5--preparing the block A by using the block
B as polymerization initiator, and 6--removing or polymerizing by
conventional radical polymerization techniques the residual monomers
which may be present in the copolymer thus obtained.

[0064] When the residual monomers of the blocks A and/or B are removed by
polymerization using well known conventional radical polymerization
techniques, the amounts of conventional radical initiator, such as, for
example, an organic peroxide or an azo compound, and the polymerization
conditions, such as, for example, the temperature, have to be chosen so
as to ensure that the conventional radical homopolymers of the monomers A
and/or B have molecular weights such that they will be predominantly
incorporated in the corresponding blocks A and/or B of the block
copolymer prepared by controlled radical polymerization, according to the
above description. This is necessary in order to prevent the chains of
conventional homopolymers A and/or B obtained from the residual monomers
of the block polymerization from forming new phases separate from the
phases A and B of the block copolymer, which would result in a
morphological modification which may be reflected by a poorer adhesive
performance of the final adhesive composition. The nitroxides used in
this process correspond, for example, to the formula (III) below:

##STR00001##

in which: R and R', which are identical or different and which are
optionally connected so as to form a ring, denote C1-C40 alkyl
groups optionally substituted by one or more hydroxyl, alkoxy or amino
groups, R and R' preferably denoting, independently, an unsubstituted
C1-C10, more preferably C1-C6, alkyl group, such as a
tert-butyl group, and RL denotes a monovalent group with a molar
mass of greater than 16 g/mol, such as a dialkyl phosphonate group and in
particular a diethyl phosphonate group.

[0065] In addition, the block copolymer which can be used according to the
invention can be obtained commercially from Arkema under the trade name
Nanostrength®.

Grafting

[0066] In another embodiment of the invention, the copolymer which is a
subject matter of the invention can be obtained by grafting associative
groups to a block copolymer already formed comprising at least one
reactive functional group, such as an acid, anhydride, alcohol,
mercaptan, amine, epoxy or isocyanate functional group, preferably an
anhydride functional group, by reaction of one or more modifying agents
carrying, on the one hand, an associative group and, on the other hand, a
reactive group chosen from amine, mercaptan, epoxy, isocyanate, anhydride
or alcohol groups, preferably an amine group, said reactive group being
capable of forming a covalent bond with said reactive functional group.

[0067] The anhydride functional group carried by the copolymer can be
obtained in two ways. It can be introduced either during the
polymerization, with a monomer preferably of maleic anhydride type, or
after the polymerization; this method of obtaining is described
subsequently. The addition of anhydride during the polymerization is
preferred; when this route is not possible or possible only with
difficulty, the formation of anhydride on the polymer is chosen.

Introduction or Formation of Anhydrides

[0068] In this embodiment, anhydrides are grafted to the copolymer. The
copolymer can, for example, be a styrene/butadiene/styrene block
copolymer where the soft block has been hydrogenated. Maleic anhydride is
subsequently grafted to this soft block by radical reaction using, for
example, peroxides. This reaction can be carried out in an extruder.

[0069] In this other embodiment, anhydrides are formed on the copolymer.
The copolymer carrying reactive functional groups can, for example, be a
methyl methacrylate/butyl acrylate/methyl methacrylate (also denoted
MMA/BUA/MMA) block copolymer including anhydride functional groups. This
block copolymer can be obtained from a block copolymer of alkyl
(meth)acrylate, in particular methyl (meth)acrylate, and of butyl
(meth)acrylate, functionalized with (meth)acrylic acid, for example
including between 0.5 and 15 mol % of (meth)acrylic acid units. Such a
block copolymer functionalized with (meth)acrylic acid is subsequently
treated in order to obtain the anhydride functional groups according to a
cyclization process, preferably under basic catalysis conditions, which
can in particular be carried out in an extruder. The preferred basic
catalysts include sodium hydroxide and sodium methoxide, CH3ONa. The
cyclization can be carried out by passing the starting copolymer through
a single- or twin-screw extruder with the catalyst and optionally other
additives, such as lubricants, antioxidants or colorants; the extrusion
temperature can be between 200 and 300° C. and preferably greater
than 250° C. One or more extrusion passes can be carried out in
order to obtain the desired level of cyclization (formation of glutaric
anhydride). The degree of cyclization can be controlled in order to
adjust the content of anhydride functional groups obtained, which can,
for example, range from 0.1 to 20 mol % per block comprising the
anhydride functional groups.

Modifying Agents

[0070] The reactive and associative groups respectively of the modifying
agent can be separated by a rigid or flexible chain composed of from 1 to
30 carbon atoms, some at least of which can be substituted, and
optionally of one or more heteroatoms chosen in particular from sulfur,
oxygen and nitrogen, said chain optionally including one or more ester or
amide bridges. The chain is preferably a linear or branched
C1-C10 alkylene chain optionally interrupted by one or more
nitrogen atoms, more preferably a linear C1-C6 alkylene chain.

[0071] The modifying agent can thus correspond to any one of the formulae
(B1) to (B4):

[0074] Some of these compounds can be obtained by reaction of urea with a
polyamine. For example, UDETA, UTETA and UTEPA can respectively be
prepared by reacting urea with diethylenetriamine (DETA),
triethylenetetraamine (TETA) and tetraethylenepentaamine (TEPA).

[0075] The number of associative groups carried by the copolymer in this
embodiment according to the invention can be simply adjusted by varying
the amount of modifying agent or the reaction time and reaction
temperature. It is generally preferable for the amount of modifying agent
to represent from 0.1 to 15% by weight, more preferably from 0.5 to 5% by
weight, with respect to the weight of the copolymer carrying reactive
functional groups, and/or for the mean number of associative groups per
copolymer chain to be between 1 and 200 and preferably between 1 and 30.

[0076] In a preferred embodiment of the invention, the mean number of
associative groups per copolymer chain is greater than or equal to 3,
preferably between 3 and 200 and entirely preferably between 3 and 30.

[0077] The grafting process is carried out by reacting the modifying agent
and the copolymer carrying reactive functional groups. This stage can be
carried out in the molten state, for example in an extruder or an
internal mixer, at a temperature which can range from 100° C. to
300° C., preferably from 150° C. to 280° C. and even
from 200° C. to 280° C. The modifying agent is blended with
the polymer, alone or using an additive which makes possible the
impregnation of the solid polymer grains by the premelted modifying
agent. The solid blend, before introduction into the extruder or the
mixer, can be rendered more homogeneous by cooling in order to cause the
modifying agent to solidify. It is also possible to meter the latter into
the extruder or the mixer after the polymer to be grafted has started to
melt. The time at the grafting temperature can range from a few seconds
to 5 minutes. The modifying agent can be introduced into the extruder in
the form of a masterbatch in a polymer which can be the polymer to be
grafted. According to this method of introduction, the masterbatch can
comprise up to 30% by weight of the modifying agent; subsequently, the
masterbatch is "diluted" in the polymer to be grafted during the grafting
operation. According to another possibility, the grafting can be carried
out by reaction in a solvent phase, for example in anhydrous chloroform.
In the latter, the reaction temperature can range from 5° C. to
75° C., for times ranging from a few minutes to a day, and at
concentrations of polymer before grafting of between 1 and 50% by weight,
with respect to the total weight of the solution. Depending on the
solvent chosen, the temperature of the grafting reaction can vary between
5° C. and 150° C. and preferably between 25° C. and
100° C.

[0078] It has been demonstrated that the copolymer which is a subject
matter of the invention makes it possible to improve the hot adhesion
between two supports.

[0079] Another subject matter of the present invention is thus the use of
a copolymer carrying associative groups as described above for improving
the cohesive and adhesive behavior as a function of the temperature of
the adhesive compositions in which it is included, making it possible to
result in a very good thermal stability.

[0080] Thus, a copolymer carrying associative groups as described above
can be used to improve the adhesion and/or the shaping of the adhesive;
in other words, a bonding is obtained at a lower temperature for the same
effectiveness, which makes it possible to reduce the amount of tackifying
resin to be used in order to have the desired properties.

[0081] The addition of these associative groups can also make it possible
to improve the cohesion of the adhesives and to render the layer of
adhesive stronger, in order, for example, to limit the tearing thereof
when a stress is applied. Unlike the known crosslinked adhesives, the
adhesive which is the subject matter of the present invention can be
reshaped at high temperature by virtue of its thermally reversible bonds.
These associative groups can also confer, on the adhesive, a better
resistance to solvents.

[0082] Another subject matter of the present invention is the use of an
adhesive as described above in the manufacture of labels or of adhesives
for binding two sheets or layers of paper together or else one sheet or
layer of paper with another object, such as a bag made of plastic or of
plastic-coated paper, of structural or repairing hot-melt adhesives which
can be used in the construction industry, do-it-yourself, the manufacture
of objects, including hygiene articles, such as disposable diapers or
towels, also including constituent parts of vehicles, boats or airplanes,
also including articles of clothing or decoration, such as shoes,
clothes, furniture and decorative objects, including office automation
articles, such as paper carriers or lamps, and also any other application
requiring the assembly of two surfaces without the use of a liquid
vehicle (water or solvent). It will also be possible, by virtue of the
hot-melt adhesives of the invention carrying associative groups, to
produce bondings on difficult supports, such as cardboard and/or floor
coverings.

[0083] A better understanding of the invention will be obtained in the
light of the following examples, given solely for the purposes of
illustration and which do not have the aim of restricting the scope of
the invention defined by the appended claims.

[0085] Reaction is allowed to take place for 90 min at ambient temperature
and with stirring and then the reaction medium is filtered. The toluene
filtrate is washed twice with 1.5 l of a saturated aqueous NH4Cl
solution.

[0086] A yellowish solid is obtained, which solid is washed with pentane
in order to give 51 g of
2-methyl-2-[N-(tert-butyl)-N-(1-diethoxyphosphoryl-2,2-dimethyl-propyl)am-
inoxy]propionic acid (yield: 60%). The structure is in particular
confirmed by mass spectrometry and 1H NMR spectrometry.

Preparation of a Dialkoxyamine

[0087] 2 g of the monoalkoxyamine obtained as described above, 0.52 g of
1,4-butanediol diacrylate with a purity >98% (1 equ.) and 6.7 ml of
ethanol are introduced into a 100 ml round-bottomed flask purged with
nitrogen. The mixture is heated at reflux at 78° C. for 20 h and
then the ethanol is evaporated under vacuum. 2.5 g of a highly viscous
yellow oil are obtained.

[0088] The 31P NMR analysis shows the complete disappearance of the
monoalkoxyamine (27.4 ppm) and the appearance of the dialkoxyamine
(multiplet at 24.7-25.1 ppm). The analysis by mass spectrometry of
electrospray type reveals a weight of 961 (M+).

Preparation of the Block Copolymer

[0089] The synthesis is carried out in 2 stages: [0090] 1st stage: Bulk
preparation of a living poly(n-butyl acrylate) polymer

[0091] 146 g of butyl acrylate, 7.68 g of methacrylic acid and 3.93 g of
the dialkoxyamine obtained as described above are introduced into a 2 l
polymerization reactor equipped with a variable-speed stirrer motor, with
inlets for the introduction of the reactants, with branch pipes for the
introduction of inert gases which make it possible to drive off the
oxygen, with probes for measuring the temperature, with a system for
condensation of vapors with reflux and with a jacket which makes it
possible to heat/cool the contents of the reactor by virtue of the
circulation in the jacket of a heat-exchange fluid. After degassing
several times with nitrogen, the reaction medium is brought to
115° C. and this temperature is maintained by thermal regulation
for several hours.

[0092] Samples are taken throughout the reaction in order to: [0093]
determine the polymerization kinetics by gravimetric analysis
(measurement of solids content), [0094] monitor the change in the
number-average molecular weight (Mn) as a function of the conversion of
the monomer to polymer.

[0095] When a conversion of 70% is reached, the reaction medium is cooled
to 60° C. and the residual butyl acrylate is removed by
evaporation under vacuum.

[0098] 478 g of methyl methacrylate and 1028.7 g of toluene, which are
degassed beforehand, are added at 60° C. to the poly(n-butyl
acrylate) prepared above. The reaction medium is then heated at
105° C. for one hour and then at 120° C. for an additional
hour. The conversion reached is of the order of 50%. After returning to
ambient temperature, the solution of copolymer (methyl
methacrylate-b-n-butyl acrylate-b-methyl methacrylate) comprising 50% by
weight of n-butyl acrylate is withdrawn from the reactor and the residual
monomers and solvents are removed by evaporation under vacuum.

[0099] The molecular weights of the copolymer as polystyrene equivalent
are 139 800 g/mol for Mn (number-average molecular weight) and 285 192
g/mol for Mw (weight-average molecular weight). The polydispersity index
is 2.04.

[0100] The copolymer obtained is denoted under the reference "AG07".

1B--Formation of Anhydride

[0101] The above copolymer comprises 5% of methacrylic acid in the BUA
phase.

[0102] This copolymer is placed in an oven under vacuum at 235° C.
overnight in order to form anhydrides (reaction between a methacrylic
acid unit and a butyl acrylate unit or between two methacrylic acid
units).

[0103] The copolymer obtained is denoted under the reference "AG12".

1C--Blending of the Block Copolymer with UDETA by Coextrusion

[0104] The copolymer prepared as described in example 1B is blended with
UDETA under the following conditions: as the grafting reaction between
the UDETA and the anhydride formed on the MMA/BUA/MMAs is very fast, the
latter is carried out by reactive extrusion on a DSM Research®
microextruder.

[0105] The experimental protocol is then as follows:

[0106] X grams of anhydride-modified MMA/BUA/MMA and Y grams of UDETA are
weighed out in an aluminum dish. 3 blends are produced and the amounts of
X and Y are respectively: 14.85 g and 0.15 g for a degree of grafting of
1%, denoted under the reference "AG13"; 14.7 g and 0.3 g for a degree of
grafting of 2%, denoted under the reference "AG14"; and 14.25 g and 0.75
g for a degree of grafting of 5%, denoted under the reference "AG15".

[0107] In a first step, only the copolymer is introduced into the extruder
using a pneumatic piston and is then left to mix for a few minutes.

[0108] Once the mixture is very homogeneous, the liquid UDETA is
introduced via the open hopper using a pipette. The combined mixture is
subsequently left to blend for 6 minutes under the conditions given in
the following table 1:

Evaluation of the Mechanical Properties of the Copolymer According to the
Invention by Studying the Hot Adhesion (SAFT Test)

2A--Protocols of the Tests Carried Out

[0110] The SAFT test (ASTM D4498) measures the ability of an HMPSA to
withstand a static force of 0.5 kgf under the effect of a steady rise in
temperature of 0.4° C./min.

[0111] The SAFT is defined by the temperature at which separation, by
parallel vertical slippage, may be observed of an area of 25×25
mm2, coated with copolymer as obtained in example 1, from a flat
sheet of board.

[0112] A film of copolymer is pressed at 190° C. for 2 minutes
between two sheets of silicone-treated paper under a force of 400 daN. A
square of 25×25 mm2 is subsequently cut out and placed between
two test specimens made of board and pressed at 190° C. under 400
daN for 2 minutes. The test strips had to be conditioned for at least 4
hours before the test in a climate-controlled chamber at 23±2°
C. and 50±5% RH. The self-adhesive tape is applied using a
standardized standard 2 kg roller.

2B--Results Obtained

[0113] The results thus obtained are combined in the following table 2:

[0114] The oven is heated up to a temperature of 170° C.; the
samples for which "did not drop" is mentioned reached this temperature
without the two sheets of board becoming detached.

[0115] It is observed that the copolymers which are subject matters of the
invention exhibit a better hot adhesion between two supports, in
comparison with copolymers not in accordance with the invention not
carrying an associative group based on nitrogenous heterocycle.

Patent applications by Francois Genes Tournilhac, Paris FR

Patent applications by Ludwik Leibler, Paris FR

Patent applications by Manuel Hidalgo, Brignais FR

Patent applications by Nicolas Dufaure, Bernay FR

Patent applications by Arkema France

Patent applications by Centre National De La Recherche Scientifique (CNRS)